This riddle inherently requires an outside-the-box solution, which always makes it amusing when someone claims “No, that’s not the correct outside-the-box solution; this one is”. They’re not thinking outside the proverbial box; they’re just thinking inside a different box.
Of course, even the simplest inside-the-box solution as the OP has phrased it still gives you a 2 in 3 chance of guessing right, which is pretty good odds for winning a free house.
For ages, my mom’s house had a dummy switch in the living room (in the middle of a three-switch panel, between two functional switches), and also had a lighting fixture in the living room ceiling that had no means of turning on. A couple of years ago, she finally found a way to connect them to each other without ripping out the entire ceiling.